1. Field of the Invention
The present invention relates to a process for preparing estrogen derivatives, such as 17-halogenated 19-norsteroids, and also to the intermediate compounds prepared during the implementation of this process.
2. Description of the Art
Osteoporosis is a bone disease which affects 50 million individuals throughout the world, more particularly women. Its development is age-related and most commonly begins after the menopause. This disease is characterized by a decrease in bone density, and results in deformations, vertebral compression and, ultimately, spontaneous fractures. Osteoporosis therefore represents a serious risk to public health. The main treatment consists in regularly taking estrogens, which decreases the bone loss but which, however, can be accompanied by certain side effects (bleeding, hot flushes, risk of breast cancer, etc.). A new series of molecules, called SERMs (Selective Estrogen Receptor Modulators), enables the treatment of osteoporosis while at the same time avoiding some of the side effects.
Patent application WO 99/67274 describes molecules having a 19-norsteroid structure, which are halogenated in the 17-position. Also, disclosed therein is a process of preparation of these compounds involving the halogenation at the end of the synthesis. The synthesis has now been optimized in the present invention:                by reducing the number of steps with the steroid substrate;        by carrying out the halogenation right at the beginning of the synthesis in order to make the purification easier.        
All of the references described herein are incorporated herein by reference in their entirety.